Manufacture of papers having low affinity for adhesives



Patented May 7, 1940 PATENT OFFICE MANUFACTURE or PAPERS HAVING LOWAFFINITY FOR ADHESIVES Florian ,Strovink, Medford, Mesa, assignor toBennett Incorporated, Cambridge, Mass., a corporation of MassachusettsNo Drawing.

Claims.

tape from undue coalescence or blocking and' hence permits such tape tobe readily unrolled and separated therefrom with the adhesive coatingcomposition in the desired intact and adhesive condition. Again, thepaper product of the present invention may be used as an insulating orseparating medium between uncured or sticky rubber sheets and othersticky articles in a stack. It afiords an excellent and inexpensivesubstitute for so-called Holland cloth, which is sometimes used forfacing adhesive tape or sheet material to be stored or packaged in rollform and which is removed from the adhesive face when the tape or sheetmaterial is put to its intended adhesive use. a

In accordance with the present invention, a

paper base is filmed or protected on its surface with soap or equivalentmaterial deposited thereon from aqueous solution or suspension moreparticularly after the base has been primed or filmed with wax in theform of an aqueous wax emulsion containing water-wettable binder andthen dried. The soap or equivalent exposed filming substance imparts to'the'paper product the desired low afiinity for adhesive surfaces,especially for those of rubberyand/or resinous nature. The waxy primingfilm, which also has low aflinity for such adhesive surfaces,constitutes a desirable background for the exposed surface film, sinceit ensures separation of the paper from an adhesive surface even whenthe exposed surface fllm is imperfect in the sense that it is abraded orotherwise impairedin its adhesive-insulating quality. The waxy primingfilm also prevents the soap, which is applied to the paper in the formof an aqueous solution or suspension, from being largely dissipated inthe paper body, especially when a waterleaf or slight- In other words,the priming film promotes concentration or confinement of the soapsolution on the paper surface, whereat the soap exercises 55 its desiredfunction. The water-wettable binder ly sized paper base is used asstarting material.

Application September 10, 1938, Serial No. 229,315

forming part of the aqueous priming emulsion not only bonds together thesurface fibers of the paper base and thus prevents such fibers frombeing plucked out or separated from the base and fouling the adhesivesurface or coating 5 of a tape or other body as it is being removed fromthe paper product hereof but also imparts to the waxy priming filmsufficient water-wettable or water-absorbable quality so thatit ispossible to retain in and on such film enough aqueous soap solution orsuspension to furnish an exposed surface film of the desired substantialweight and adhesive-insulating quality.

While not limited thereto, the present invention will now be describedin terms of particular compositions and treatments that may be used inpreparing a paper product of the desired adhesive-insulating quality,for instance, for facing the sticky, rubber-containing and/orresin-containing coating on rolled tape intended for masking, surgical,and other purposes. The paper base used as starting material may beordinarywaterleaf or body-sized paper of any suitable basis weight, forinstance, about 25 to pounds basis weight, and composed of any suitablepapermaking stock, which may be beaten to such degree as is consistentwith good formation or substantially homogeneous texture in the papersheet made therefrom. A waterleaf kraft paper sheet of about 30 poundsbasis weight is typical of the kind of base satisfactory for thepurposes hereof. The priming composition may be applied to such sheet asit is being delivered progressively from the dry end of a papermakingmachine or as it is being progressively withdravm from a rollaccumulation. Thus, the waterleaf sheet may be passed through a bath ofthe priming composition, and excess composition removed therefrom, as bypassage through squeeze rolls, whereupon the primed sheet may beredried, as by passage over one or more steamheated drier rolls.

A satisfactory priming composition may be prepared by admixing one part(by volume) of aqueous wax emulsion of about 30% wax content with abouttwo parts. of sodium silicate of about 40 Baum and about'one part ofwater. The aqueous wax emulsion,.whose wax content may be paramn oramorphous mineral or hydrocarbon wax, should preferably be stabilized bysuch agents as keep it from breaking or precipitating unduly whenadmixed with the comparatively large amount of concentrated silicatesolution. Since wax emulsionsprepared with only fatty acid soap asemulsifying agent tend to break or precipitate under such conditions,they are distinctly less desirable than wax emulsions containingstabilizers practically inert toward sodium silicate, for instance, suchwax emulsions as are stabilized with neutral salts of sulphonic acids,preferably sodium or other alkali metal salts of such acids, orwater-soluble gums of the nature of gum arabic. Wax emulsions of thislatter kind do not break or precipitate when mixed with comparativelyconcentrated sodium silicate solution in any and all such proportions asmay be desired for the purposes hereof. Upon passing a waterleaf papersheet of about 30 pounds through the silicate-wax composition described,the sheet may be squeezed to retain, say, about 10% to 20% of absorbedsolids, based on the dry weight of the starting or original sheet.

Although sodium silicate is a preferred water soluble binder in thepriming composition hereof because it is comparatively inexpensive andimparts to the priming film the desired waterwettability whileappropriately binding together the surface fibers of the paper, it maybe replaced in part or in entirety by other binders. Thus, it ispossible to replace part or all ofthe sodium silicate solution in thepriming composition described by an equal volume of cooked aqueousstarch solution of 3% starch content, for instance, a cooked tapiocastarch solution or the like, to which may have been added preparatory tocooking a small amount of causticsoda or other alkali to promoteswelling or gelatinization of the starch granules. It is also possibleto use albuminous binder solutions, such as casein or glue solutions, inlieu of, or together with, the silicate and/or starch solutions. Theaqueous wax emulsion may be stabilized essentially by fatty acid soapwhen it is admixed with a binder solution, such as alkaline starch orcaseinate solution, having little or no tendency to break or upset asoap-stabilized wax emulsion.

The predried, primed paper sheet is filmed or coated with soap, as bypassing such sheet through a bath of soap solution or suspension or byapplying the soap solution or suspension to such sheet on calenderrolls, and drying the solution-wet or suspension-wet sheet to depositsoap in and on the underlying priming film, which confines the soap verylargely to the paper surface. It might be noted that the water-wettablebinder content of the priming film is suflicient to impart to the driedpriming film the desiredsubstantially uniform pickup of soap from thesoap solution or soap suspension. Were the priming film. composed onlyof wax, the wax would tend to repel an aqueous soap solution orsuspension and hence limit unduly the amount of solution picked up bythe priming film; and such pickup as did occur would be apt to be"spotty or non-uniformly distributed over the priming film. A typicalsoap solution useful on,

a calender stack for the purposes hereof may be a potassium oleatesolution of about 25% to 30% soap content. Such a solution may beapplied to the rolls of a calender stack so that both faces of theprimedpaper sheet are filmed 'with' rate of speed may be a potassium oleatesolution of about 10% to 20% soap content. After the primed paper sheetis passed through a bath of the soap 'solutior; it may be squeezed tothe desired soap content and then redried, as on the usual steam-heateddrier drums. The various factors affecting the degree of retention ofthe soap by the paper sheet, including the concentration of the soapsolution, its temperature, the time of immersion or contact between thepaper sheet and the bath of soap solution, and the degree of pressureexerted-by the squeeze rolls, may be coordinated to lead to a finishedor dried paper product containing about 1% to 3% or more soap, based onthe weight of the starting or original paper sheet. If desired, part orall of the water-soluble soap of the aqueous soap composition may bereplaced by such water-insoluble soaps as zinc or aluminum stearates,palmitates, or other heavy metal fatty-acid soaps, in which latter casethe water-insoluble soap occurs as a fine suspension or dispersion inthe aqueous medium. When a water-insoluble or heavy metal fatty-acidsoapjs used, it is preferably applied to the paper in the form of adispersion or suspension in water-soluble fatty-acid soap solution,'

Both the soluble and water-insoluble fatty acid soaps as absorbed anddeposited in and on the priming film from aqueous solution orsuspension, furnish upon drying a protective paper film of the desiredlow aflinity for adhesive surfaces or coatings, for instance,permanently adhesive coating compositions containing rubber and/orresin. There are various compounds of soaplike or detergent characterwhich may be applied in aqueous solution or suspension to a primed paperbase 'with results similar to those realized with the fatty acid soaps.Among such compounds maybementioned the sulphonated or sulphatedaliphatic fatty or higher alcohols, such as the acid sulphuric acidesters of lauryl alcohol, cetyl alcohol, and stearyl alcohol and thesodium or other salts of such sulphonated or sulphated fatty or higheralcohols; also the sulphonated naphthenic acids and the sulphonatednaththenates or the salts of the sulphonated naphthenic acids. Thesulphonated or sulphated fatty alcohols are sometimes regarded as theacid sulphuric acid esters of hydroxy-fatty acids; and it is perhaps notamiss to consider such acid esters and the sodium or other salts thereofas soaps and likewise to consider.the..-sulphonated fied as soaps, theyfunction for the purposes hereof much in the same way as fatty acidsoaps and are hence equivalents of the fatty acid soaps. Accordingly, itis to be understood that, unless otherwise qualified, the term soap isused in the appended claims in a comprehensive sense to include notonlythevarious saponifled fatty acids but also sulphonated oil soaps, suchas sulphonated castor oil soap, and the various compounds obtained'bysulphonating oils, fatty acids, naphthenic acid, the higher or-fattyaliphatic alcohols, either in the form of such compounds or after theirneutralization with suitable sodium, potassium, or other alkali metal,alkaline earth metal or heavy'metal compound.

The illustrative compositions or treatments hereinbefore describedaresusceptible of considerable change or modification without departingfrom the scope of the instant invention as defined by the appendedclaims. Thus, the priming composition may be varied as regards itsconcentration and the relative proportions of water-soluble binder andemulsified wax present therein; and the amount of priming solidsdeposited" on the paper surfaces, may also vary, depending uponsuchfactors as the basis weight of the paper sheet being treated, itsporosity or absorbency, etc. In some instances, the priming compositionmay contain fillers of the nature of clay and calcium carbonate, but itis usually desirable to avoid the presence of a substantial amount offiller in the priming film by reason of the fact that a filler detractsfrom the strength of such film and may weaken such film to an extentsuch that it may be partly or locally stripped from the paper sheet uponseparation of the sheet from an adhesive surface, thereby fouling theadhesive surface undesirably. Again, the concentration of the soapsolution or suspension for depositing theexposed soap film is subject toconsiderable variation, depending, for example, upon whether the paperis passed through a bath of the soap solution or suspension or whetherthe soap solution or suspension is applied to the paper on calenderrolls, upon the soap-retentivity of the priming film, upon the basisweight ofthe paper base, etc. Generally speaking, it is preferable thatthe soap be deposited fromsolution or suspension in and on the primingfilm in-an amount upwards of about 1%,based on the weight of the paperbase, but the amount of soap may be even less than 1% when the paperbase is comparatively heavy and falls into the category of paperboard,for instance, is of a weight upwards of about 100 pounds. It ispreferable to avoid a starting paper sheet or base of drastically orhighly calendered character, since a highly calendered paper sheetevidently presents what may be termed a casehardened superficial fibrouslayer or skin of lower tear-resistance than the internal body or layersof the sheet; and, upon removal of a finished paper product hereofcomprising a highly calendered paper base from an adhesive surface.fragments of the relatively weak surface layer or skin may be locallystripped from the internal paper body with attendant undesirablefoulingof the adhesive surface.

The particular mode of applying to the paper sheet the priming and/orsurfacing compositions is also subject to variation. For instance,either or both such compositions may be applied to the paper sheet inthe form of a spray from suitable spray nozzles or in the form oi. afilm from a suitable applicator roll rotating partially submerged in abath of composition. Again, the priming composition may be applied tothe paper sheet at any suitable stage of traverse of'the sheet on thepapermaking machine, for instance. to the still-moist paper web beforeit enters the drier section of the papermaklng machine, to the partiallydried paper sheet at an intermediate 'Thus, the procedure may involvethe application of the priming composition to the still-moist papersheet by means of a so-called size tub stationed at anintermediate stagein the drier section and the application of the soap or surfacingcomposition on a pair of rolls of the calender stack located immediatelyafter the drier section, the predried, primed sheet receiving thecomposition from such rolls as it is passing through such rolls andbeing redried as it passes through'hot rolls forming part of the stack.

It is possible to produce a finished paper product satisfying therequirements hereof by applying to the paper base a single compositioncontaining the ingredients of both the priming and surfacingcompositions hereinbefore described, particularly when the soap of thesurfacing composition is compatible with the ingredients of the primingcomposition, as when the aqueous priming composition containsessentially emulsified wax and such binder substances as cooked starch,glue, casein, or equivalent albuminous material. In such latter case,the application of a single composition to the paper base' followed by adrying of the paper base protected on its surface with the requisiteamount of wax, binder, and soap results in a dried paper product havingthe desired low affinity for adhesives. However, the use of a singlecomposition is generally less satisfactory than the application ofseparate priming and surfacing compositions as hereinbefore described,for it is preferable that the soap ingredient, which is especiallystick-resistant or of low adhesive affinity, be kept undiluted ratherthan be diluted or adulterated by the binder and/or wax. In other words,by the two-step procedure hereinbefore described, it is possible todeposit the soap as a separate entity or film on the surface of thepaper sheet, even though some of the soap does penetrate into thepriming film when the soap-surfaced sheet is dried under heat. On theother hand, the use of a single composition containing the soap as wellof soap-and its fragility or low cohesive strength that renders itstick-resistant or of low adhesive afiinity. The wax evidently hassimilar properties and also evidently serves to modify the bindercontentof the priming film so that, although the binder substance exercises thedesired bonding effect on the surface fibers of the paper base, it isdiluted sufficiently by the wax to part readily from an adhesive surfaceeven when the overlying soap film is abraded, cracked, or otherwiseimpaired. Irrespective of whether such explanation for the behavior orutility of the paper product hereof is correct, it is a fact that it isreadily separable from adhesive surfaces, after having served as aprotective or facing medium thereon, with no appreciable foulin of suchadhesive surfaces or 'detraction from the tenacity'of adhesion ofsuchsurfaces to other surfaces with which they are intended to be adhesivelyunited.

It might be noted that the initial treatment of the paper base or sheetwith the aqueous composition comprising water-soluble binder andemulsified wax is attended by infusion of the binder and the wax intothe paper at least at its surface fibers and that subsequentdrying ofthe paper, which is effected at an elevated temperature above themelting point of the emulsifiedparaflin wax or equivalent waxy material,promotes more or less fusion of the wax and its penetration into thepaper body. The extent to which the paper body is penetrated by thebinder and wax may vary, depending, for example, upon the porosity orabsorbency of the pape base and the viscosity of the aqueous primingcomposition. In any event, the priming composition fills the surfacepores or voids of the paper and deposits on the paper surfaces a smoothpriming film penetrating more or less into the paper body. Such a filmaffords a substantial barrier against penetration into the paper body ofsoap from aqueous solution or suspension even though such film is not sowater-repellent as to prevent soap from being absorbed and/or adsorbedthereon in substantial amount from.aqueous solution or suspension.

I claim:

l. A paper adapted for use as a readily separable protective medium onadhesive surfaces. said paper carrying as a distinct entity an exposedsoap film and being infused at least at its surface fibers underlyingsaid soap film with wax and water-wettable binder, which afford asubstantial barrier against the penetration of said paper by said soapfilm.

2. A paper adapted for use as a readily separable protective medium onadhesive surfaces,

said paper carrying as a distinct entity an exposed scap film and beinginfused at least at its surface fibers underlying said soap film withwaxy material, which affords a substantial barrier against thepenetration of said paper by said soap film. I v

3. A paper adapted for use as a readily separable protective medium onadhesive surfaces,

said paper carryin an exposed film comprising water-soluble fatty acidsoap and water-insoluble fatty acid soap and also an underlying primingfilm of wax and water-wettable binder substance bonding together itssurface fibers.

4. A paper adapted for use as a readily separable protective medium onadhesive surfaces, said paper carrying an exposed film comprisingwatersoluble fatty acid soap and also an underlying priming film of waxand water-wettable binder substance bonding together its surface fibers;

5. A paper adapted for use as a readily separable protective medium onadhesive surfaces, said paper carrying an exposed film comprisingwater-insoluble fatty acid soap and also an underlying priming film ofwaxand water-wettable binder substance bonding together its surfacefibers.--

6. A paper adapted for use'as a readily separable protective medium onadhesive surfaces, said paper carrying an exposedfilm of fatty acid soapand also an underlying priming film of wax and sodium silicate. I 4

7. A paper adapted for use as a readily separable protective medium onadhesive surfaces, said paper carrying an exposed film offatty acid soapand also an'underlying priming film of wax and starch., I

8. A paper adapted for'use as a readily separable protective medium onadhesive surfaces, said paper carrying an exposed film of fatty acidsoap and also an underlying film of wax and water-wettable albuminousbinder.

9. A method of producing paper adapted for use as a readily separableprotective medium on adhesive surfaces, which comprises priming a papersheet with an aqueous composition comprising einulsified wax andwater-soluble binder, drying the primed sheet, surfacing the dried sheetwith aqueous soap composition, and redrying the surfaced sheet.

10. A method of producing paper adapted for use as'a readily separableprotective medium on adhesive surfaces, which comprises priming a papersheet with an aqueous composition containing silicate, emulsified wax,and an emulsifying agent for the wax practically inert to'the sodiumsilicate; drying the primed sheet;' surfacing the dried sheet withaqueous soap composition; and redrying the surfaced sheet.

I FLORIAN STROVINK.

